Method for encapsulating an electronic component using a foil layer

ABSTRACT

The invention relates to a method for encapsulating an electronic component, in particular a semiconductor, fixed on a carrier, comprising the processing steps of: a) placing at least one foil layer in a mould, b) placing the carrier in contact with the foil layer with the side remote from the component, and c) encapsulating the electronic component with encapsulating material, wherein the foil layer undergoes a treatment whereby the adhesion of the foil layer is increased such that it adheres to the carrier. The invention also relates to a foil material for applying during such a method.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for encapsulating an electroniccomponent, in particular a semiconductor, fixed on a carrier comprisingthe processing steps of: a) placing at least one foil layer in a mould,b) placing the carrier in contact with the foil layer with the sideremote from the component, and c) encapsulating the electronic componentwith encapsulating material. The invention also relates to a foil forapplying such a method.

2. Description of the Prior Art

The International patent application WO 00/66340 discloses a method formanufacturing encapsulated electronic components including the shieldingof a side of the support of electronic components with an adhesive film.In a specific embodiment the adhesive film comprises an adhesive layerthat becomes adhesive as a result of an increase in temperature of thefilm in the mould. This method has the problem that the duration of theprocessing step of moulding the electronic components includes the timeto make the film adhesive, furthermore the level of adhesion of the filmis difficult to control.

The encapsulating of electronic components, in particular semiconductorproducts, is a precisely controlled process wherein use is generallymade of so-called transfer moulding. An object for (partial)encapsulation is herein placed in a mould. Liquid encapsulating materialis forced into the mould by means of one or more plungers, wherein oneor more mould cavities preformed in the mould are filled withencapsulating material. After curing of the encapsulating material themould is opened and the product (partially) encapsulated withencapsulating material is taken out of the mould. In order to preventthe encapsulating material adhering to the mould, use is made inparticular applications of an additional foil layer for placing in themould. The encapsulating material is herein carried between the foillayer and the product for (partial) encapsulation. The encapsulatingmaterial thus remains separated from the mould.

When one or more housings manufactured from encapsulating material arearranged on a flat carrier, the encapsulating material can be forcedunilaterally against the carrier and the opposite side of the carrierremains free of encapsulating material. In many products it is of greatimportance that this side remote from the encapsulating material remainsfree of encapsulating material, among other reasons because of thecontact positions with which it must be possible to later connect theproduct for electrical conduction. However, an increasing number ofproducts are being applied wherein the carrier is provided withopenings/recesses through which, if specific measures are not taken, theencapsulating material can get to the side of the carrier which is to bekept clean. The solutions for preventing this are, among others, toapply the encapsulating material on one side in the still unopenedposition of the carrier followed by removal of a material layer from thecarrier (for instance by means of etching) after the encapsulatingmaterial has been applied. It will be apparent that this includesadditional treatments, which has the effect of increasing costs. Afurther solution in practice is, prior to applying encapsulatingmaterial, to adhere a protective layer against the carrier provided withopenings. The openings in the thus treated (assembled) carrier areclosed. The closed carrier can now be (partially) encapsulated. Afterthe (partially) encapsulated carrier has been removed from the mould,the protective layer is removed from the carrier once again. A problemhere is making the contact side of the (partially) encapsulated productproperly clean again. This method also has the effect of considerablyincreasing costs.

The International patent application WO 00/66340 discloses a method formanufacturing encapsulated electronic components including the shieldinga side of the support of electronic components with an adhesive film. Ina specific embodiment the adhesive film comprises an adhesive layer thatbecomes adhesive as a result of an increase in temperature of the filmin the mould. This method has the problem that the duration of theprocessing step of moulding the electronic components includes the timeto make the film adhesive, furthermore the level of adhesion of the filmis difficult to control.

The object of the present invention is to provide a method and means forencapsulating an electronic component, in particular a semiconductor,fixed on a carrier, wherein a contact side of the carrier is kept fee ofencapsulating material in economic and controlled manner.

SUMMARY OF THE INVENTION

The invention provides for this purpose a method for encapsulating anelectronic component, in particular a semiconductor, fixed on a carrier,comprising the processing steps of: a) placing at least one foil layerin a mould, b) placing the carrier in contact with the foil layer withthe side remote from the components, and c) encapsulating the electroniccomponent with encapsulating material, characterized in that the foillayer undergoes a treatment whereby the adhesion of the foil layer isincreased such that it adheres to the carrier. The term “treatment” ishere understood to mean a treatment or process which is to a greater orlesser extent physical. Instead of a complex pre-treatment of thecarrier, a foil layer is now simply placed in the mould. This is asimple operation in which much experience has already been acquired inpractice. The special feature of the invention is now that theproperties of the foil are influenced such that the foil layer adheresto a greater or lesser degree to the side of the carrier remote from theside to which the encapsulating material must be applied. Instead of acomplex pre-treatment or post-treatment of the carrier to prevent thisbeing permeable to encapsulating material, use is simply made accordingto the invention of the existing technology of placing a foil layer inthe mould. The word “treatment” is understood to mean a treatment orprocess which the carrier undergoes that is to a greater or lesserextent physical. When the foil layer and carrier are brought into mutualcontact, the correct force can thus be exerted immediately to realizethe desired connection. The number of processing steps hereby remainslimited. On the other hand it is also possible, when specific conditionsrequire, to place the foil and the carrier in mutual contact and onlythen to increase the adhesion of the foil. It is furthermore noted thatit can be advantageous during arranging of the foil to vacuum the spacebetween the carrier and the foil, this to prevent inclusion of gases.The present invention furthermore has the advantages that it providesfreedom in choice of the type(s) of adhesion-increasing treatment(s) andthat it provides freedom in the duration of the adhesion-increasingtreatment. As the adhesion-increasing treatment is a process step thatis separated from the processes that take place in the mould it is alsobetter to control and to monitor than the adhesion-increasing treatmentaccording the prior art.

The adhesion-increasing treatment can for instance comprise atemperature increase of the foil, optionally combined with corona,plasma or like treatment with a similar effect. Traditionally thesurface tension of the foil is influenced with a corona treatment, buttest results indicate that it is also possible to influence the adhesionof foil material with a corona treatment. Results have been obtainedherein during tests wherein after an adhesion-increasing treatment hasbeen carried out the foil adheres particularly to a contact surface ofthe carrier consisting at least substantially of copper. In addition tothe examples mentioned here, other treatments of the foil can of coursealso be envisaged, such as for instance exposure or a chemicaltreatment.

In a preferred application of the method the foil undergoes a subsequenttreatment after encapsulation of the electronic component withencapsulating material, whereby the adhesion of the foil layer isdecreased such that it adheres less to the than during encapsulation ofthe electronic component with encapsulating material. Such a treatmentfor reducing adhesion can for instance comprise a temperature decreaseof the foil. With such a subsequent treatment the foil can be releasedmore readily from the carrier and there is less chance of foil residuebeing left behind on the carrier.

For a simple supply of the foil, it can be unwound from a roll and thenmoved through the mould. Such a method can be at least partially takenover from the prior art method for processing of foil. In anotheradvantageous application of the method according to the invention, thefoil can be used a number of times; a fail which has been used once doesnot have to be discarded but can be refused. This has the advantage,among others, that the costs of using the foil can be reduced and thatthe method has less of an environmental impact.

It is recommended to place the foil layer only shortly before applyingthe encapsulation. This reduces the risk of damage to the foil materialby previous processing steps. An example hereof is the connection of theelectronic component by means of connecting wires (wire bounding) whichtakes place at relatively high temperatures (usually 240-260° C.). Afurther advantage of the method according to the invention is that it ispossible to thus process assembled carriers of for instance acombination of ceramic and metal, wherein the chance of damaging suchcarriers (“crack”) is also reduced.

The invention also provides a foil for applying the above describedmethod, characterised in that the foil comprises a carrier layer havingarranged there an adhesive layer which can be activated. The adhesivelayer which can be activated can for ice comprise a thermoplasticplastic, while the carrier layer can consist of paper. Conversely, it isalso possible for the carrier layer to consist of plastic. Yet anotheroption is that the carrier layer consists of a non-ferrous metal. Thisof course also includes alloys, for instance alloys with aluminium. Theadvantages as described above can be realized with such a foil. The foilcan be manufactured relatively cheaply and costs can be further reducedwhen the foil is reusable. Advantageous results have been obtained inpractice with an adhesive layer of polypropylene/polyethylene which canbe activated and which has a melting range at about 140° C. It is ofcourse necessary to opt for an adhesive layer that can be activatedwhich is inert to many substances.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further elucidated with reference to thenon-limitative embodiments show in the following figures. Herein:

FIG. 1A shows a schematic side view of a carrier provided with anelectronic component, in which carrier there are openings,

FIG. 1B shows a schematic side view of the carrier of FIG. 1A, nowhowever an adhesive foil has been arranged on the side remote from theelectronic component so as to thus close the openings in the carrier,

FIG. 1C sows a schematic side view of the carrier of FIGS. 1A and 1B,now however after an encapsulation on has been arranged round theelectronic component,

FIG. 1D shows a schematic side view of the carrier of FIGS. 1A, 1B and1C, now however after the foil has been removed from the carrier, and

FIG. 2 shows a schematic view of route followed by a foil material froma roll during an advantageous embodiment variant of the method accordingto the

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1A shows a carrier 1 in which through-openings 2 are present.Placed on carrier 1 is an electronic component 3 which connects tospecific parts of carrier 1 by means of connecting wires 4. FIG. 1Bshows that a foil layer 5 is arranged against carrier 1 such that theopenings 2 are hereby closed. For a good closure of openings 2 it isimportant that foil layer 5 fits properly onto carrier 1. If there isnot a good connection been the foil layer 5 and carrier 1 there is afterall the risk of (a function of) encapsulating material to be appliedlater passing between foil layer 5 and carrier 1, whereby d side ofcarrier 1 remote from the electronic side is contaminated and properprocessing of the electronic component lame becomes difficult orimpossible.

FIG. 1C shows carrier 1 with foil layer 5 after an encapsulation 6 hasbeen arranged around electronic component 3. This encapsulation 6 isconstructed from a liquid encapsulating material (for instance epoxy)which subsequently cures. Finally, FIG. 1D shows carrier 1 withencapsulation 6 after the foil layer 5 is removed from the carrier. Itwill be apparent that this removal is only possible once theencapsulation 6 is substantially cured. It is of great importance thatfoil layer 5 is removed such that the free side of carrier 1 is cleanthe removal.

FIG. 2 shows a schematic representation of the method according to thepresent invention. Foil 8 is unwound from a roll 7 in a directionaccording to arrow P1. Foil material 8 then undergoes a schematicallyshown treatment 9 (for instance a corona treatment, a plasma treatmentand/or a heat treatment and/or a chemical treatment) whereby theadhesion is increased, at least on one side. Electronic components 10are then brought into contact with the activated foil material 8. Afterpassing an encapsulating device 11 the adhesion of the foil material 8can be reduced once again during a treatment 12 (optional). Anencapsulated electronic component 13 can hereby be released relativelyeasily from the deactivated foil material 8. The remaining deactivatedfoil material 8 is wound onto a roll 14. Depending on the situationcondition it is possible to envisage a roll 14 with already used foilmaterial being utilized again during the present method.

1. A method for encapsulating an electronic component, in particular asemiconductor, fixed on a carrier, comprising the processing steps of:a) placing at least one foil layer in a mould, b) placing the carrier incontact with the foil layer with the side remote from the component, andc) encapsulating the electronic component with encapsulating material,wherein the adhesion of the foil layer is increased in combination withencapsulation of the electronic component, wherein the adhesion of thefoil layer is increased with a separate adhesion-increasing treatmentbefore placing the foil layer in the mould according to processing stepa).
 2. The method as claimed in claim 1, wherein the foil layerundergoes the adhesion-increasing treatment before the carrier isbrought into contact with the foil layer.
 3. The method as claimed inclaim 1, wherein the adhesion-increasing treatment comprises atemperature increase of the foil.
 4. The method as claimed in claim 1,wherein the adhesion-increasing treatment comprises a corona treatmentor plasma treatment.
 5. The method as claimed in claim 1, wherein afterthe adhesion-increasing treatment is performed, the foil adheresparticularly to a contact surface of the carrier consisting at leastsubstantially of copper.
 6. The method as claimed in claim 1, whereinthe foil undergoes a subsequent treatment after encapsulation of theelectronic component with encapsulating material, whereby the adhesionof the foil layer is decreased such that it adheres less to the carrierthan during encapsulation of the electronic component with encapsulatingmaterial.
 7. The method as claimed in claim 6, wherein the treatment forreducing adhesion comprises a temperature decrease of the foil.
 8. Themethod as claimed in claim 1, wherein the foil is unwound from a rolland then moved through the mould.
 9. The method as claimed in claim 1,wherein the foil is used a number of times.
 10. Foil for applying themethod as claimed in claim 1, wherein the foil comprises a carrier layerhaving arranged thereon an adhesive layer which can be activated. 11.Foil as claimed in claim 10, wherein the adhesive layer which can beactivated comprises a thermoplastic plastic.
 12. Foil as claimed inclaim 10, wherein the carrier layer consists of paper.
 13. Foil asclaimed in claim 10, wherein the carrier layer consists of plastic. 14.Foil as claimed in claim 10, wherein the carrier layer consists of anon-ferrous metal.
 15. Foil as claimed in claim 10, wherein the foil isreusable.